We are commanded to "honor" our mother and father (Exodus 20:12). The Church, which is the Body of Christ, exists on earth and in heaven. We on earth are still struggling but those believers in heaven are triumphant and holy. We honor our parents on earth and even if they're in heaven, we should still honor them. We can still talk to them. By extension, we can also honor the other souls in heaven, since they are our elder siblings in God's big family. (What's forbidden, by the phrase "contacting the dead", is attempting to gleen preternatural information from spirits, as an end-run around God. This is sorcery or necromancy. King Saul was guilty of this.) Note Genesis 12:3, God says to Abram "And I will bless them that bless thee, and curse him that curseth thee..." By this we see that God is pleased, and blesses us, when we bless & honor those whom He has blessed. Just because Abraham is no longer on earth doesn't mean we can't still honor him for his willing cooperation in God's salvation plan. Scripture nowhere says don't honor the souls in heaven. It just says do not talk to spirits of the dead. In the Old Covenant all the departed were "dead". The righteous and the unrighteous dead were in Sheol, awaiting the coming of the Messiah. The righteous dead were not part of the Body of Christ yet. Then Jesus came, died, descended to Sheol, and brought the righteous dead to life in Heaven, leaving behind the unrighteous dead (they are those "dead" whom we are forbidden to contact). The souls in Heaven, however, are now more alive than we are, and are of the same Body of Christ as we, so we can and should honor them as God's perfected creatures.
These terms (honor, venerate, respect) don't imply divinity in the target. "Praying" to a soul in heaven is not necessarily worship. Petitional prayer, requesting someone in heaven to pray for me, is the same as my asking my friend to pray for me. It is no different. The Kingdom of God (aka the Church) is a family affair, some on earth and some in heaven. Paul directs Christians to pray for others in 1Timothy 2:1 "I EXHORT therefore, that, first of all, supplications, prayers, intercessions, and giving of thanks, be made for all men;". ALL Christians, collectively, form the one Body of Christ (1Corinthians). This means we on Earth are of the same Body as the saints in Heaven. Hebrews 12 describes the souls in Heaven observing us on earth ("cloud of witnesses"). Revelation 5 and 8 depict the prayers of the saints (Christians) being offered up to God by angels in Heaven. So, asking someone in Heaven to pray for me is plainly Scriptural.
Reverence = Honor/respect or worship, or adore, depending on context
Reverence is used in KJV in reference to our biological fathers (Hebrews 12:9), to spouses (Ephesians 5:33) and in reference to God (Hebrews 12:28). Logically, then, these are two degrees of reverence. Just like honor, or even worship, we give supreme reverence (supreme honor, supreme worship, adoration) to God alone, and lesser reverence (lesser honor, lesser worship) to our parents and, by extension, our elders in the faith (be they fathers or bretheren). 1Chron29:20 demonstrates this concept of degrees of worship, they "bowed down their heads, and worshipped the LORD, and the king".
Worship
Modern popular usage of the term "worship" is in the context of worship as due to God alone (=adoration), but historically, it didn't always imply divinity in the target. It used to mean giving honor ("worth-ship", worthy of honoring) to someone (Greek: dulia) or, when given to God, was considered "supreme" worship such that was due to Him alone (adoration, Greek: latria). Context determines any application's meaning. Refer to Le Morte d'Arthur. You'll find men being "worshiped" yet not treated like God. Even in Scripture it is sometimes used regarding a mortal (1Chron29:20) "And David said to all the congregation, Now bless the Lord your God. And all the congregation blessed the Lord God of their fathers, and bowed down their heads, and worshipped the Lord, and the king.". It was a common usage in the 1400's and even later. Church documents, which are all originally in Latin, in English translation might use the word "worship" regarding some person. In relation to anyone besides God, it means the lesser meaning. Such a document in Greek would use "dulia" in relation to a person and would use "latria" in relation to God.
Adoration
From Latin "adoro". Generally means giving worship and thanks and praise and glory and honor and offering sacrifices to someone as the SOURCE of love,life, blessings,grace,salvation, etc. This degree of worship is rightly due to God alone, since He alone is those things.
English "idolatry" comes from Greek εἰδωλολατρία (idololatria). This means giving adoration, as due to God alone, to an object or person. Hence, giving lesser honor/worship to a Saint is not idolatry. It is "idoloduly". (Did I just invent a new word in English? I'm sure someone else put that together before I did.)
Venerating or honoring a soul in Heaven (usually it's a canonized Saint) is not de facto worship/adoration and so is not in violation of the Commandment against idolatry (1st or 2nd, depending on the numbering scheme). But if someone is doing so, treating the Saint as God, as a source of Life/Salvation or asking supernatural information or offering sacrifices to them, then that is adoration and idolatry, giving to a non-God entity the worship & honor due to God alone, and is forbidden by Scripture & Catholic dogma.
Some Christians object to the Catholic practice of bowing near a painting or statue while praying to Mary (or another Saint). This, they claim, is in violation of the Commandment in Ex20:5 which prohibits making idols to worship. Scripture does forbid bowing down to worship idols/people/things/angels/dem
Catholics bowing down near a picture or statue are not worshiping a lifeless image but are honoring that which it represents. The Saint represented, most notably Mary, is worthy to be thus honored (that is her "worth-ship") because God has honored her first, with His abundant grace, and she allowed His grace to do great things to and through her (God wouldn't have forced her to mother His child). We honor (worship, in the lesser sense) Mary and the souls in heaven, but ONLY to God do we give supreme worship, ONLY God do we adore as the source of Life and Love and our Savior.
Another way to look at the action of kneeling while in prayer to a Saint (petitioning a Saint to pray for us) is that we are not really kneeling in respect to the Saint, but instead we are kneeling WITH the Saint in respect to God, giving shared worship and adoration to God.
The Communion of Saints is the term used to describe the interaction of all believers, earth-bound (the Church Militant) and Heaven-dwelling (the Church Triumphant). Not to mention the saints undergoing their final purification, the last application of Jesus' cleansing Blood (the Church Suffering), before joining the Church Triumphant. The Church Suffering cannot help themselves or others, but the Churches Militant and Triumphant can pray and sacrifice for them. 1John5 describes how saints should pray for those guilty of venial ("sin not unto death"), but not mortal ("sin unto death"), sins. This verse obviously applies to earthly believers but it also describes the Church Suffering, since they are being cleansed of lingering attachments to sin which they did not shed while alive on earth.
References:
King James Bible used for Scripture references:
http://www.jesus-is-lord.com/thebible.htm
Saints: Holy Siblings
http://zuserver2.star.ucl.ac.uk/~vgg/rc/aplgtc/hahn/m4/sts.html
Mary in the Word of God
http://www.salvationhistory.com/studies/lesson/queen_a_biblical_introduction_to_mary
Do Catholics Worship Statues?
http://www.catholic.com/tracts/do-catholics-worship-statues
Le Morte d'Arthur:
http://www.sacred-texts.com/neu/mart/
Catholic Encyclopedia: Dulia
http://www.newadvent.org/cathen/05188b.htm
Catholic Encyclopedia: Latria
http://www.newadvent.org/cathen/09036a.htm
Catholic Encyclopedia: Honour
http://www.newadvent.org/cathen/07462a.htm
Catholic Encyclopedia: Adoration
http://www.newadvent.org/cathen/01151a.htm
Catholic Encyclopedia: Worship
http://www.newadvent.org/cathen/15710a.htm
Catholic Encyclopedia: Veneration of Images
http://www.newadvent.org/cathen/07664a.htm
Catholic Encyclopedia: Idolatry
http://www.newadvent.org/cathen/07636a.htm